The European Union has accused Belarusian strongman Alexander Lukashenko of facilitating the wave of migrants and refugees, mainly from the Middle East, in retaliation for sanctions imposed by Brussels. NATO on Monday slammed Minsk for using the migrants as political pawns.

"Interior ministry forces and soldiers managed to stop the first mass attempt to breach the border," Poland's defence ministry tweeted.

"Migrants have set up a camp in the Kuznica region. They are constantly guarded by Belarusian services."

Polish border guards posted video footage on Twitter showing migrants using wire cutters and branches to breach a razor-wire border fence as Polish officials in riot gear looked on.

Polish government spokesman Piotr Muller told reporters that 3,000-4,000 migrants were near the Polish border and that Warsaw expected an escalation of attempts to breach it, also with the use of arms.

"We expect that there may be an escalation of this type of action on the Polish border in the near future, which will be of an armed nature," Muller said.

Muller blamed "people linked to Belarusian special services" for organising the breach. A Polish government crisis unit was handling the response.

NATO slammed as "unacceptable" Belarus's use of migrants to put pressure on the EU, saying it was worried about "escalation" on the border with Poland.

The EU vowed action in the face of a "hybrid threat". Talks were under way on "amendments of the existing Belarusian sanctions regime and adjusting this regime to the new threats", European Commission spokesman Peter Stano said.

- Deaths -

Minsk has reportedly issued special visas allowing migrants to fly into Belarus from Iraq among other Middle Eastern states.

The sanctions were imposed after Belarus diverted a flight between EU capitals in May to arrest a dissident journalist and his girlfriend on board, and for a brutal crackdown on the opposition.

Lukashenko has denied the charges. Belarus border services insisted that the migrants posed no threat.

"All these people, including women and children, do not pose a threat to security and do not behave aggressively," Belarus border official Anton Bychkovsky told Belarus's BelTA news agency on Monday.

"According to the refugees, they gathered together in such a large group to prevent their forced expulsion by Poland, as well as to draw the attention of the international community to non-observance of human rights by Poland," Bychkovsky added.

Poland has sent thousands of soldiers to the border area, enforced a state of emergency in the region complete with a media blackout, built a razor-wire fence and approved the construction of a wall.

Caught in the middle, migrants often report being forced to cross the border by Belarusian officials and then being pushed back into Belarusian territory by Polish authorities.

At least 10 migrants have died in the region, including seven on the Polish side of the border, according to the Polish daily Gazeta Wyborcza.

- 'Hybrid attack' -

"We're prepared for any scenario," Poland's Interior Minister Mariusz Kaminski tweeted on Monday, adding that Warsaw had beefed up numbers of police and soldiers in the area.

Videos published on Twitter by the Nexta Belarusian opposition media outlet, showed hundreds -- if not thousands -- of people in winter clothing carrying backpacks and walking along a road.

According to a geolocation check by AFP's fact-checking service, one of the videos was taken near buildings in Bruzgi, Belarus, about 1.2 kilometres (three-quarters of a mile) from Poland's Kuznica border crossing. The signs along the road were in Belarusian.

Belarusian opposition leader Svetlana Tikhanovskaya blamed Lukashenko for orchestrating a "hybrid attack" and called on the United Nations Security Council to "discuss this crisis" in a Monday tweet.